The present invention relates to an intracranial pressure relief valve and, more particularly, to a simplified valve construction including coaxially aligned valve part members which establish three stage valve operation to provide either constant pressure or constant flow characteristics in accordance with a fluid pressure differential applied across the valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles resulting in an abnormal increase in both epidural and intradural pressures. This in turn may cause a number of adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Treatment of a hydrocephalic condition frequently involves relieving the abnormally high intracranial pressure. Accordingly, a variety of CSF pressure regulator valves and methods of controlling CSF pressure have been developed which include various check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage location in the body such as the venous system of the peritoneal cavity. Check valves operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined value.
The use of a simple check valve can be advantageous with respect to minimizing the cost of the valve, but with nothing more than check valve operation, the treatment of hydrocephalus is potentially disadvantageous since it is possible for such valve to open in response to a sudden, but nevertheless perfectly normal, increase in differential pressure between CSF in the ventricular spaces and fluid at the selected discharge location of the body, resulting in abnormal and potentially dangerous hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, resulting increased vertical height of the fluid column existing between the head and the selected drainage location may result in such an increase in differential pressure. Accordingly, valves, such as that described in the copending application of the present inventor, Ser. No. 672,868, filed Nov. 19, 1984, have been developed which serve to prevent undesired hyperdrainage by limiting the flow rate of fluid through the valve when a sudden increase in differential pressure occurs.
In this valve, a diaphragm, movable in response to the pressure differential between ventricular CSF pressure and pressure of fluids at the drainage location of the body, was mechanically coupled to a valve seat having a fluid metering orifice extending therethrough. The orifice allowed passage of CSF from the ventricular spaces to the selected drainage location. Motion of the diaphragm in response to change in the differential pressure caused the valve seat to be moved from a first position, in which the valve seat contacted a suitably located sphere to block and thereby prevent the passage of fluid through the orifice, to a second position, in which a generally cylindrical fluid flow restrictor partially occluded the orifice, thereby limiting fluid flow therethrough. By controlling the position of the sphere, the valve seat and the restrictor, it was possible to construct a valve having flow characteristics which avoided hyperdrainage with sudden changes in differential pressure.
As valves of this type are miniaturized, the number of parts involved, the complexity of the configurations of the various parts and the cost of generating the same become major factors. Working tolerances involved are on the order of 0.001 of an inch and continuing efforts are being made to reduce manufacturing costs while maintaining rather complex effective functioning.
The present invention is directed to an improvement in such a valve wherein the more standard types of valve elements or parts are utilized, the accumulated knowledge available in the manufacture of such parts being relied upon to reduce the cost of the valve. Basically, the preferred form of valve constructed in accordance with the present invention utilizes a sphere spring held against a valve seat somewhat similar to the well known type of check valve, the flow characteristics of the valve in response to variations in differential pressure being controlled by a restrictor element of simplified construction and cooperating with the check valve sphere in a unique manner to effectively provide the various modes of operation in the treatment of hydrocephalus.
In view of the foregoing, it is a general object of the present invention to provide a new and improved pressure regulator valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a pressure regulator valve which includes components which may be easily and economically manufactured.
It is a still more specific object of the present invention to provide a pressure regulator valve in which critically dimensioned components are of an easily manufactured configuration.